Conventionally, laser machining devices for laser machining a workpiece, which is a plate-shaped object to be worked on, to cut out a plurality of products move a machining head to a machining position of the next product each time laser machining of a product is completed for sequential laser machining.
An operation of bringing a machining head that has moved to a machining position close to a workpiece is called an approach operation. In the approach operation, by monitoring an electrostatic capacitance profiling voltage that varies depending on the distance between a nozzle provided at the machining head and a workpiece, the machining head is positioned in a position in which the nozzle is at a first distance from the workpiece.
During the approach operation, after the machining head approaches the workpiece until the distance between the nozzle and the workpiece becomes a second distance larger than the first distance, the amount of travel of the machining head per control period is decreased as the distance from the workpiece becomes smaller, so that the machining head can be positioned with high accuracy in a position in which the nozzle is at the first distance from the workpiece. The travel speed of the machining head when the nozzle is at the second distance or more from the workpiece is called an approach speed, and a ratio used for determining the amount of travel per period after the distance between the nozzle and the workpiece becomes less than the second distance, a gain.
The detection range of the electrostatic capacitance profiling voltage is fixed at a circular region of a fixed size centered around the machining head. Therefore, when the approach operation is performed in a peripheral edge portion of a workpiece, for example, the workpiece is present only in a part of the detection range. In the state where the workpiece is present only in a part of the detection range, even when the distance between the machining head and the workpiece is the same, the electrostatic capacitance profiling voltage decreases, compared to a case where the approach operation is performed in a central portion of the workpiece. Consequently, when the approach operation is performed in the peripheral edge portion of the workpiece with the approach speed and the gain set the same, the machining head is positioned where the distance between the nozzle and the workpiece smaller than the first distance. In that case, an occurrence of an overshoot causes the nozzle to strike the workpiece. When the nozzle strikes the workpiece, it is required to move the machining head away from the workpiece and then bring it close to the workpiece so that the approach operation takes time.
A technique intended to prevent overshoots during an approach operation is disclosed in Patent Literature 1.
An invention disclosed in Patent Literature 1 determines a positional deviation amount, the difference between a position command and the actual position of a servomotor, and changes a position gain to a corrected position gain based on the positional deviation amount to avoid striking of a nozzle on a workpiece due to an overshoot.